Abstract

Background and aims

Many plant-beneficial microorganisms can influence secondary plant metabolism, but whether these effects add up when plants are co-inoculated is unclear. This issue was assessed, under field conditions, by comparing the early impacts of seed inoculation on secondary metabolite profiles of maize at current or reduced mineral fertilization levels.

Methods

Maize seeds were inoculated singly with selected strains from bacterial genera Pseudomonas and Azospirillum or mycorrhizal genus Glomus, or with these strains combined two by two or all three together. At 16 days, maize root methanolic extracts were analyzed by RP-HPLC and secondary metabolites (phenolics, flavonoids, xanthones, benzoxazionoids, etc.) identified by LC/MS.

Results

Inoculation did not impact on plant biomass but resulted in enhanced total root surface, total root volume and/or root number in certain inoculated treatments, at reduced fertilization. Inoculation led to qualitative and quantitative modifications of root secondary metabolites, particularly benzoxazinoids and diethylphthalate. These modifications depended on fertilization level and microorganism(s) inoculated. The three selected strains gave distinct results when used alone, but unexpectedly all microbial consortia gave somewhat similar results.

Conclusions

The early effects on maize secondary metabolism were not additive, as combining strains gave effects similar to those of Glomus alone. This is the first study demonstrating and analyzing inoculation effects on crop secondary metabolites in the field.

Notes

Acknowledgments

This work was supported in part by the European Union (FW6 STREP project MicroMaize 036314). We are grateful to Pierre Castillon (Arvalis, Bazièges, France) and Arvalis staff at the Pouzol Etoile experimental station for implementation of the field trial. We thank Bachar Blal (Agrauxine, Quimper, France) and Aleš Látr (Symbio-M, Lanškroun, Czech Republic) for providing formulated microbial inoculants and MPN data, and Geneviève Défago (ETH Zürich) for discussions. This work made use of the platform DTAMB (IFR 41) in Université Lyon 1.